Modern disc drive designs use digital feedback control systems to control the position of the head with respect to the tracks on the recording surface of the disc. Because disc drives and their electrical control systems, like all complex physical systems, are susceptible to resonance at particular frequencies, the feedback control system that is used to control the movement of the actuator arm generally employs one or more digital notch filters at some point in the feedback loop. These digital notch filters must be calibrated to attenuate the particular resonant frequencies of the particular disc drive in which the filters are used. In other words, a set of constant coefficients for each digital notch filter must be determined so that the filter attenuates an actual resonant frequency of the disc drive.
Since the resonant frequencies of disc drive may vary from drive to drive, it is not sufficient to find a single set of coefficients for a given design. Rather, each disc drive must be individually calibrated. At present, this calibration process generally takes place at the time of media certification, which is when the manufacturer uses the assembled drive to scan the recording media for defects and marks defective disc sectors as unusable. Manufacturers run a series of tests to determine the resonant frequencies of the drive. The disc drive, in turn, uses these resonant frequencies to look up filter coefficients in a table of coefficient values for various frequencies and programs its notch filters using the coefficients retrieved from the table.
Table lookup, however, requires that all coefficient values be stored in memory. This makes it more complicated and costly to obtain precise filter coefficient values for a given design, since finer levels of precision require more firmware memory to store more filter coefficient values. What is needed, then, is a way to achieve precise filter calibration while minimizing memory usage. The present invention provides a solution to this and other problems, and offers other advantages over previous solutions.